Standard explosives, and applications of explosives such as warheads and mining boreholes, are designed to perform a specific task by detonating. Detonation is defined as a supersonic reaction rate which is propagated as a shock through the explosive material. In the case of an explosive warhead, detonation of the explosive is designed to produce a set of lethal effects such as fragmentation of the warhead casing, thermal effects from the heat of detonation and blast effects from the shock that is generated by the detonation.
More specifically, when detonation is initiated in one end of a warhead, typically a cylindrical explosive charge, the detonation travels through the explosive at speeds of over 20,000 feet per second. The detonation results in both a very rapid generation of gas from the explosive and the transfer of momentum to the warhead casing material, which may be made of, for example, steel. The steel casing is rapidly expanded and breaks up into small pieces due to the action of the rapid pressurization and momentum transfer. A steel case will break up into long strips initially and the strips will then break up into short high velocity fragments. Standard warhead is normally initiated at a single point on one end along the axis of the warhead. The detonation propagates down the length of warhead producing roughly equal fragment sizes and energy in all directions perpendicular to the axis of the warhead, albeit with a small induced “Taylor” angle in the direction of detonation propagation.
Sometimes the destructive effects from a given warhead design are more lethal than is actually required for a specific target situation. However, it is not feasible to design a warhead for each and every situation on the battlefield, nor is it logistically possible to provide such an array of warheads where they are needed during battle. In many cases it may be impossible to complete a bombing mission with a large bomb that is readily available due to the likelihood of unintended damage, while a smaller bomb is not available at the time. This either limits the use of high value assets such as bomber aircraft or may endanger friendly ground forces from collateral damage. Additionally, more and more wars are being fought in urban areas, as terrorist and guerilla forces locate their headquarters and forces in the midst of civilian populations. Therefore, there is a need for the ability to tune the output of a given warhead design so that it can address multiple situations that occur during battle.
It has been shown that bombs and warheads can be made to have tunable destructive effects by first initiating a deflagration or combustion in the high explosive and then initiating a detonation from an opposite end of the high explosive
A different and perhaps more useful approach to controlling lethal effects from an explosive warhead is to utilize a carefully designed pattern of detonators within and outside of the casing of the warhead. It has been known for many years that the fragmentation energy from a warhead may be enhanced in a given direction by changing the initiation pattern in the warhead. The initial application for this technology appears to have been for air-to-air missile warheads, where a near-miss was a common occurrence and warhead directionality was thought to be vital to maintaining lethality.
It is most advantageous to have a directed limited concentrated fragmented charge, which provides for a powerful charge in a limited area, thus avoiding collateral damage, thereby limiting harm to civilians, friendly soldiers, and preventing unnecessary damage to infrastructure, while at the same time increasing “targeted” lethality to allow for the destruction of the intended target.
DE 004139373C1 (Held) discloses a fragmentation warhead having a main explosive charge in a fragmentation casing which is closed at both ends by end plates. Deformation charges which extend in the longitudinal direction are arranged partly around the fragmentation casing. The fragmentation casing and the main explosive charge are designed to be deformable in order to force the fragmentation casing inwards before fragmentation formation when the deformation charge is detonated on the side facing the target. In order to achieve a situation in which the fragmentation casing is forced in approximately flat on detonation of the deformation charge which faces the target, the fragmentation casing is designed such that it can tear off in the region of the two end plates on detonation of the deformation charge.
FR2704638 (Broussoux et al.) discloses an explosive fragmentation weapon having a grooved outer shell with its inner surface at least partly surrounding the explosive charge and its outer surface grooved to form the fragments on detonation. At least some of the outer surface grooves contain an electrically-conducting material with a shape memory effect, elongated in shape and with ends connected selectively to a power supply. The grooves containing the material are rectangular in cross section with two grooves to one of the surfaces of the shell, and a base which lies parallel to it and has a slit in it. The material with the shape memory effect is a copper/nickel/aluminum alloy, and the grooves lie along the meridians or parallels of the shell.
U.S. Pat. No. 6,8484,642 (Kuhns et al.) discloses a fragmentation body for fragmentation projectiles and warheads, including an integral fragmentation shell structure made of cast metal, and the shell structure having an outer wall surface and an inner wall surface separated by a thickness of the shell, where at least one of the inner or outer surfaces includes recesses formed through part of the thickness of the shell to define a plurality of fragments which remain integrated with the shell structure until an explosive force is detonated in proximity of the shell, wherein the shell material comprises a steel alloy including carbon, chromium, nickel, molybdenum, cobalt, and the balance essentially being iron. Shell structures of the inventive fragmentation body also have a fragmentation pattern defined via recesses or grooves provided in at least one of the inner or outer wall surfaces thereof to define the size and shapes of the fragment projectiles desired. The steel alloy used is high strength, yet controllably fragmentable into desired and uniform individual projectile shapes and sizes, and in a desired overall dispersion pattern, during case break up.
U.S. Pat. No. 3,820,461 (Wilhelm et al.) discloses a fragment layer for a warhead having a longitudinal axis comprising: a plurality of axially adjacent, annular rings of preformed fragments, each said ring being coaxial with said axis and encompassing the periphery of said warhead; an annular retaining layer covering the outside surface of said rings to secure said fragments in position; and annular explosive layer disposed between said rings and the periphery of said warhead; and means for selectively detonating said explosive layer to generate a low velocity disc pattern of fragments.
U.S. Pat. No. 4,026,213 (Kempton) discloses a cylindrical warhead having an outer, relatively-thin metal skin member and an inner thicker metal casing, the main explosive charge being disposed in the space between the members with associated boosters or charge initiators. The initiators include a first set of circumferentially-spaced aiming detonation members and a second set of similarly spaced main charge-firing members. Aiming is achieved by first firing a selected aiming initiator to produce a force sufficient to rupture and break open an arcuate section of the outer warhead skin but insufficient to produce a main charge detonation. Next, a main charge-firing initiator disposed substantially diametrically opposite the ruptured arcuate section is fired to produce an inwardly-directed main-charge blast for fragmenting the thicker inner casing and driving the fragments in the desired direction through the ruptured arcuate section.